1. Field of the Invention
The present invention relates to an organic light emitting display device capable of representing white light, and a method of fabricating the same.
2. Description of the Related Art
An organic light emitting display device includes a substrate, an anode disposed on the substrate, an emission layer (EML) disposed on the anode, and a cathode disposed on the emission layer. In the organic light emitting display device, when a voltage is applied between the anode and the cathode, holes and electrons are injected into the emission layer and recombined to create excitons. The excitons transition from an excited state to a ground state, thereby emitting light.
To display full colors, an organic light emitting display device can include emission layers corresponding to red (R), green (G), and blue (B), respectively. However, such red, green and blue emission layers of the organic light emitting display device have different luminance efficiencies (Cd/A). These different luminance efficiencies cause the red, green and blue emission layers to emit light at different brightness. Generally, the brightness of the emission layer is approximately proportional to a current. Therefore, when the same current is applied, one color light may be emitted to have a relatively low brightness but another color light may be emitted to have a relatively high brightness, so that it is difficult to have proper color balance or white balance. For example, the luminance efficiency of the green emission layer is from three to six times higher than those of the red and blue emission layers, so that more current should be applied to the red and blue emission layers to adjust the white balance.
To enhance white balance, an organic light emitting display device has been proposed which includes an emission layer formed to emit monochromic light (i.e., white light), and a color filter layer to filter light corresponding to a predetermined color of light from the emission layer (or a color conversion layer to convert the light emitted from the emission layer into a predetermined color of light).
FIG. 1 is a cross-sectional view of a conventional top-emission organic light emitting display device.
Referring to FIG. 1, a substrate 100 is provided, and a first electrode 110 having a reflection layer is formed on the substrate 100. Further, a thin film transistor and a capacitor may be provided between the first electrode 110 and the substrate 100.
An organic layer 120 including an emission layer is formed on the first electrode 110. The emission layer may be a single layer structure or a multiple layer structure. Further, a second electrode 130, which is transflective, is formed on the organic layer 120.
In this conventional top-emission organic light emitting display device, a resonance effect occurs due to the transflective second electrode 130. In addition, in the case where the white emission layer and the color filter are used to realize full colors, red, green and blue emission layers are stacked adjacent to one another and employed as the white emission layer. However, white light is not properly realized because of the resonance effect due to the transflective second electrode 130. Further, the resonance effect causes light to be emitted with different wavelengths according to viewing angles. Such a resonance effect largely depends on the thickness of the organic layer, so that a wavelength band of the filtered light varies according to thickness distribution of the organic layer, thereby making color and brightness representation unstable.